Underground conduits are widely used for the transmission of fluids, such as in pipelines and the like, as well as for carrying wires and cables for the transmission of electrical power and electrical communication signals. While the installation of such conduits is time consuming and costly for locations where the each can be excavated from the surface, the routing of such conduits becomes more difficult where such surface excavation cannot be done due to the presence of surface obstacles through which the excavation cannot easily proceed. Such surface obstacles include highways and railroads, where the installation of a crossing conduit would require the shutdown of traffic during the excavation and installation. Such surface obstacles also include rivers, which present extremely difficult problems for installing a crossing conduit, due to their size and the difficulty of excavation thereunder.
Prior methods for the installation of conduits have included the use of directional drilling for the formation of an inverted underground arcuate path extending between two surface locations and under the surface obstacle, with the conduit installed along the drilled path. A conventional and useful method for installing such underground conduits is disclosed in U.S. Pat. No. 4,679,637, issued Jul. 14, 1987, assigned to Cherrington Corporation, and incorporated herein by this reference. This patent discloses a method for forming an enlarged arcuate bore and installing a conduit therein, beginning with the directional drilling of a pilot hole between the surface locations and under a surface obstacle such as a river. Following the drilling of the pilot hole, a reamer is pulled with the pilot drill string from the exit opening toward the entry opening, in order to enlarge the pilot hole to a size which will accept the conduit, or production casing in the case of a pipeline conduit. The conduit may be installed during the reaming operation, by the connection of a swivel behind the reamer and the connection of the conduit to the swivel, so that the conduit is installed as the reaming of the hole is performed. Alternatively, the conduit can be installed in a separate operation, following the reaming of the pilot hole (such reaming referred to as "pre-reaming" of the hole). In cases where the conduit is installed in a separate operation, it is desirable to remove cuttings from the hole prior to installing the conduit. An examples of a hole cleaning device for removing cuttings may be found in U.S. application Ser. No. 07/789,356, to Cherrington. Additional examples of the reaming operation, both as pre-reaming and in conjunction with the simultaneous installation of the product conduit, are described in U.S. Pat. No. 4,784,230, issued Nov. 15, 1988, assigned to Cherrington Corporation and incorporated by this reference.
One problem in drilling the borehole concerns the reaming operation. The reamer includes a number of teeth which grind the earth as the reamer is pulled through the pilot hole. Cuttings from the reaming operation become lodged in the teeth and prematurely deteriorate the reamer and can cause sticking. Therefore, many reamers include a cleaning system to spray the teeth with drilling fluid to remove the debris. Unfortunately, the fluid spray from existing cleaning systems directs the debris towards the stem of the reamer and towards the front of the reamer, The debris is thus directed to areas where accumulation may occur. The accumulation is particularly troublesome in clay soils where balls of clay easily form. The balls of clay impede movement of the reamer and any attached conduit.
A second problem involves the transport of the conduit through the hole. Even where the hole is cleaned prior to installing the conduit, sticking may occur during the installation process when the pipe is drawn through the hole. While the conduit is flexible in its central portions, the leading end is relatively inflexible. Thus, curves in the hole may result in the leading edge of the conduit driving into the sidewalls of the hole. If the conduit becomes stuck in the sidewall, operations to free the conduit must be undertaken, thereby increasing the cost of the project.
Therefore, a need has arisen in the industry for installing a conduit in a horizontal hole which reduces problems associated with conduit sticking.